1. Field of the Invention
The invention relates to a coil unit, a non-contact power transmission device, a non-contact power reception device, a non-contact power supply system, and a vehicle. More particularly, the invention relates to a coil structure that reduces leakage electromagnetic fields that occur when electric power is supplied in a non-contact manner using electromagnetic resonance.
2. Description of the Related Art
Electrically-driven vehicles, such as electric vehicles and hybrid vehicles, have received much attention, as environmentally-friendly vehicles. Each of the electrically-driven vehicles is provided with a motor that generates drive power for driving the vehicle, and a rechargeable power storage device that stores electric power to be supplied to the motor. The hybrid vehicles include a vehicle provided with an internal combustion engine that serves as a power source, in addition to the motor; and a vehicle provided with a fuel cell that serves as a DC power source for driving the vehicle, in addition to the power storage device.
Among hybrid vehicles, there is a known hybrid vehicle provided with a power storage device that is charged with electric power supplied from a power source outside the vehicle, like the electric vehicles. For example, a so-called “plug-in hybrid vehicle” is known. In the plug-in hybrid vehicle, the power storage device is charged with electric power supplied from a power source at home, by connecting a power source outlet provided in a house to a charging port provided in the vehicle using a charging cable.
On the other hand, wireless power transmission has recently received attention as a power transmission method without using a power source cord or a power transmission cable. Three technologies are known as wireless power transmission technologies that are prevailing. The three technologies include a technology in which power is transmitted using electromagnetic induction, a technology in which power is transmitted using electromagnetic waves, and a technology in which power is transmitted using a resonance method.
Among them, the resonance method is a non-contact power transmission technology in which paired resonators (for example, paired resonance coils) resonate with each other in an electromagnetic field (near field), and thus, power is transmitted via the electromagnetic field. The resonance method makes it possible to transmit great electric power, that is, several kW of electric power over a relatively long distance (for example, several meters).
Japanese Patent Application Publication No. 2009-106136 (JP-A-2009-106136) describes a charging system in which electric power is transmitted to a vehicle from a power source outside the vehicle in a non-contact manner using the resonance method, and a power storage device provided in the vehicle is charged with the electric power.
Electromagnetic noise for other electrical devices may be caused due to the electromagnetic field generated around a coil unit including the resonance coil. For example, noise may be caused in a radio or the like due to the electromagnetic field. Also, when a conductor is disposed in the electromagnetic field, the conductor may be heated due to electromagnetic induction caused by the electromagnetic field, and accordingly, devices may malfunction due to temperature increase.
Therefore, when electric power is transmitted using the resonance method, it is desirable to shield, as much as possible, leakage electromagnetic fields generated in directions other than a direction in which electric power is transmitted and received.
In order to shield the leakage electromagnetic fields, shields may be disposed around a coil case in which the coil unit is housed. In this case, it may be necessary to reduce the size of the shields taking into account a space where the coil case is to be provided in the vehicle.